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Single fracture aperture patterns: Characterization by slit-island fractal analysis

Description: Single fracture measurements are difficult to obtain, but they are the only means we have to observe and study natural fracture morphology. The character of the fracture openings (apertures) is often one of the primary factors controlling fluid flow in the fracture. In particular, the shape, distribution, and connectivity of contact areas and flow channels can affect the relative permeability of wetting and non-wetting fluid phases in unsaturated systems. In this paper we use three methods of fractal analysis (the slit-island, the divider, and the variogram) as well as statistical and geostatistical analysis to characterize the geometry of measured fracture apertures obtained from two different fractured rock specimens from the field. One of these is a granitic fracture (crack) of homogeneous lithology and no displacement, the other is a fracture (fault) obtained from a highly altered fault zone, containing striations and slickensides. We discuss the fractal and geostatistical analysis of these two fractures in the context of what information is most helpful for making predictions about fluid flow in single fractures.
Date: January 1, 1993
Creator: Cox, B.L. & Wang, J.S.Y.
Partner: UNT Libraries Government Documents Department

Corrector magnets: Combined structural analysis of collider 50 mm aperture ordered wound quadrupoles interior section

Description: The 50mm aperture prototype collider ordered wound quadrupole corrector magnets have been modeled with finite element techniques considering the individual and combined load cases of the preloading from keys, cooldown to 4 K and the effect of magnetic forces during energizing. Results of the analysis are presented as longitudinal, transverse and shear stresses for the ordered wound coils and as maximum von Mises stress for the carbon steel outer laminations, the stainless steel inner lamination, and the carbon steel keys.
Date: April 1, 1993
Creator: Tran, Vu H.
Partner: UNT Libraries Government Documents Department

Compensation of RF-Induced Energy Spread in the CEBAF Injector Chopping System

Description: The CEBAF injector chopping system must generate three interleaved 499 MHz pulse trains of independently variable current from a DC input beam prior to axial compression. The chopper consists of two deflection cavities with an aperture midway between them. Lenses flanking the aperture focus the beam from the first cavity into the center of the second, where the RF deflection from the first cavity is removed. The symmetry of the RF energy spread across any time-slice of the beam is dominantly odd. The inverting optics used to focus the beam into the second cavity causes near cancellation of the energy spread from the two cavities. We present experimental measurements of the energy spread effects from a fundamental frequency (1497 MHz) chopper prototype producing a beam of suitable transverse emittance and energy spread, and discuss the expected performance of the subharmonic chopper system to be used for commissioning starting in January 1994.
Date: May 1, 1993
Creator: Tiefenback, M.G. & Krafft, G.A.
Partner: UNT Libraries Government Documents Department

Corrector magnets: Combined structural analysis of collier 50 mm aperture ordered wound dipoles interior section

Description: The 50mm aperture prototype collider ordered wound dipole connector magnets have been modeled with finite element techniques considering the individual and combined load cases of the preloading from keys, cooldown to 4 K and the effect of magnetic forces during energizing. Results of the analysis are presented as longitudinal, transverse and shear stresses for the ordered wound coils and as maximum von Mises stress for the carbon steel outer laminations, the stainless steel inner lamination, and the carbon steel keys.
Date: April 1, 1993
Creator: Tran, Vu H.
Partner: UNT Libraries Government Documents Department

Hole-Coupled Resonators Tunable Infrared Free Electron Lasers

Description: We review the study of hole-coupled resonators for broadly tunable free electron laser (FEL) applications. The mode profiles inside and outside the cavity, the diffraction losses at the mirror edges and intracavity apertures, the amount of useful power coupled through the holes, and the FEL gain are calculated for several dominant azimuthal and radial modes. The FEL interaction is taken into account by constructing a propagator similar to the Fresnel integral for free space propagation. It is found that non-confocal resonators can provide efficient hole coupling over a broad wavelength range, as long as the mode beating caused by a degeneracy in the round trip loss can be avoided. The degeneracy between the azimuthally symmetric class of modes is removed by FEL interaction, and the azimuthally asymmetric modes can be suppressed by means of intracavity apertures. Therefore, in a nonconfocal configuration, a hole-coupled resonator can be designed that is tunable over a broad range of wavelength by employing an adjustable intracavity aperture. On the other hand, confocal resonators are not suitable for hole coupling; Although mode beating does not occur in a confocal resonator, the hole coupling is difficult because the modes tend to avoid the hole. We provide a simple physical understanding of the difference in the performance of the confocal and non-confocal resonators. We also calculate and analyze the mode content of an empty resonator under continuous external mode injection. Such calculation is useful in interpreting experiments testing the hole coupling performance using CW lasers.
Date: February 1, 1993
Creator: Xie, M. & Kim, K.-J.
Partner: UNT Libraries Government Documents Department

Design for low beam loss in accelerators for intense neutron source applications

Description: Control of beam loss in intense ion linacs involves keeping beam spill below parts in 10[sup [minus]5]--10[sup [minus]8]/m by preventing total beam size from extending to the limiting apertures. Starting from good rms design practices, new analysis of the machine architecture is described in terms of the effects of the machine tune with space-charge, free-energy constraint, and halo-producing mechanisms. It is shown that halos are produced by the time- (or position-) varying nature of common linac aspects (such as misalignment, mismatching, acceleration, and construction techniques) through collective core/single-particle interaction dynamics plus resonances.
Date: January 1, 1993
Creator: Jameson, R.A.
Partner: UNT Libraries Government Documents Department

Fundamental mode rf power dissipated in a waveguide attached to an accelerating cavity

Description: An accelerating RF cavity usually requires accessory devices such as a tuner, a coupler, and a damper to perform properly. Since a device is attached to the wall of the cavity to have certain electrical coupling of the cavity field through the opening. RF power dissipation is involved. In a high power accelerating cavity, the RF power coupled and dissipated in the opening and in the device must be estimated to design a proper cooling system for the device. The single cell cavities of the APS storage ring will use the same accessories. These cavities are rotationally symmetric and the fields around the equator can be approximated with the fields of the cylindrical pillbox cavity. In the following, the coupled and dissipated fundamental mode RF power in a waveguide attached to a pillbox cavity is discussed. The waveguide configurations are (1) aperture-coupled cylindrical waveguide with matched load termination; (2) short-circuited cylindrical waveguide; and (3) E-probe or H-loop coupled coaxial waveguide. A short-circuited, one-wavelength coaxial structure is considered for the fundamental frequency rejection circuit of an H-loop damper.
Date: February 9, 1993
Creator: Kang, Y.W.
Partner: UNT Libraries Government Documents Department

Comparison of aperture determinations on RHIC for single particles tracked 10[sup 6] turns and 100 particles, having randomly generated initial coordinates, tracked for 1000 turns

Description: Aperture determinations from 100 particles tracked for 1000 turns using randomly selected initial coordinates are compared with results from 10[sup 6] turn runs when initial coordinates are defined by [epsilon][sub x] = [epsilon][sub y] and X[sub i][prime] = Y[sub i][prime] = 0. Measurements were made with ten distributions of magnetic field errors. The results from tracking 100 particles for 10[sup 3] turns are equivalent to those from 10[sup 6] turn runs, have a distribution of considerably less width, and require only one tenth the computer time.
Date: January 1, 1993
Creator: Dell, G.F.
Partner: UNT Libraries Government Documents Department

Study of stability of beam in the Fermilab main injector

Description: The Fermilab Main Injector is a new 150 GeV proton synchrotron, designed to replace the Main Ring and improve the high energy physics potential of Fermilab. The status of the Fermilab accelerator complex upgrade will be discussed. Study of the stability of the beam in the Main injector will be discussed. Detuning and corrector scheme to improve the dynamic aperture of the Main Injector will be presented. Tune modulation caused by octupolar detuning will be discussed.
Date: April 1, 1993
Creator: Mishra, C.S. & Harfoush, F.
Partner: UNT Libraries Government Documents Department

Wetting phase permeability in a partially saturated horizontal fracture

Description: A major obstacle to understanding of unsaturated fracture flow is the paucity of physical data on both fracture aperture structure and the effects of phase structure on permeability. An experimental procedure is developed for collecting detailed data on aperture and phase structure from a transparent analog fracture. Stable phase structures of varying complexity are creating within the horizontal analog fracture. Wetting phase permeability is measured under steady-state conditions. A process based model for wetting phase relative permeability is explored. Average distribution of the wetting phase is shown to provide insufficient information for modeling relative permeability; descriptive models must account for spatial structure of the phases.
Date: December 31, 1993
Creator: Nicholl, M. J. & Glass, R. J.
Partner: UNT Libraries Government Documents Department

Fundamental mode rf power dissipated in a waveguide attached to an accelerating cavity

Description: An accelerating RF cavity usually requires accessory devices such as a tuner, a coupler, and a damper to perform properly. Since a device is attached to the wall of the cavity to have certain electrical coupling of the cavity field through the opening. RF power dissipation is involved. In a high power accelerating cavity, the RF power coupled and dissipated in the opening and in the device must be estimated to design a proper cooling system for the device. The single cell cavities of the APS storage ring will use the same accessories. These cavities are rotationally symmetric and the fields around the equator can be approximated with the fields of the cylindrical pillbox cavity. In the following, the coupled and dissipated fundamental mode RF power in a waveguide attached to a pillbox cavity is discussed. The waveguide configurations are (1) aperture-coupled cylindrical waveguide with matched load termination; (2) short-circuited cylindrical waveguide; and (3) E-probe or H-loop coupled coaxial waveguide. A short-circuited, one-wavelength coaxial structure is considered for the fundamental frequency rejection circuit of an H-loop damper.
Date: February 9, 1993
Creator: Kang, Y. W.
Partner: UNT Libraries Government Documents Department

Comparison of aperture determinations on RHIC for single particles tracked 10{sup 6} turns and 100 particles, having randomly generated initial coordinates, tracked for 1000 turns

Description: Aperture determinations from 100 particles tracked for 1000 turns using randomly selected initial coordinates are compared with results from 10{sup 6} turn runs when initial coordinates are defined by {epsilon}{sub x} = {epsilon}{sub y} and X{sub i}{prime} = Y{sub i}{prime} = 0. Measurements were made with ten distributions of magnetic field errors. The results from tracking 100 particles for 10{sup 3} turns are equivalent to those from 10{sup 6} turn runs, have a distribution of considerably less width, and require only one tenth the computer time.
Date: June 1, 1993
Creator: Dell, G. F.
Partner: UNT Libraries Government Documents Department

Proposal for a feasibility study of very large aperture quadrupole magnets

Description: The authors seek expert assistance in performing a feasibility study for quadrupole magnets with inner radius at least 80 cm, field at that radius of at least 1.5 Tesla, and field integral at that radius of at least 3 Tesla-m. These magnets would be used as the spectrometer magnets in hadron-collider experiments that emphasize relatively low transverse momentum and large angular coverage, such as studies of B physics and of a variety of physics topics in the far-forward direction. The magnets would preferably be superconducting, but conventional construction may be considered as well. Should the magnets be deemed feasible, the authors then seek to initiate an R and D program to construct a prototype.
Date: April 1, 1993
Creator: Bjorken, J. D. & McDonald, K. T.
Partner: UNT Libraries Government Documents Department

Tracking studies of insertion device effects on dynamic aperture in the APS storage ring

Description: We studied the effects of an insertion device (ID) on the dynamic aperture in the 7-GeV Advanced Photon Source (APS) storage ring using the program RACETRACK. We found that the nonlinear effect of the ID is the dominant effect on the dynamic aperture reduction compared to the other multipole errors which exist in the otherwise ideal lattice. The previous study of dynamic aperture was based on the assumption that the effect of the fast oscillating terms in L. Smith`s Hamiltonian is small, and hence can be neglected in the simulation. The remarkable agreement between the previous study and the current results using RACETRACK, including all effects of the fast oscillating terms, justified those assumptions at least for the APS ring.
Date: July 1, 1993
Creator: Chae, Yong-chul & Crosbie, E. A.
Partner: UNT Libraries Government Documents Department

Beam transfer at E0: An overview

Description: The helical orbits in the Tevatron necessitated changes in the beam transfer operation between the Main Ring and the Tevatron. This document is intended to present an overview of the beam transfer with an emphasis on the recent changes. It will also serve as a bibliography for the other documents that exist on Tevatron injection.
Date: June 25, 1993
Creator: Saritepe, S. & Annala, G.
Partner: UNT Libraries Government Documents Department

Effects of transverse coupling on transverse beam size, simulation and measurements

Description: The equations of motion for particles in an accelerator lattice show that a larger physical aperture is required to hold a beam of constant invariant emittance if there is transverse coupling of the tunes. The results of a tracking simulation of particle motion in the Fermilab accumulator ring are discussed, and results are shown from beam tests carried out in the accumulator to demonstrate this effect.
Date: May 1, 1993
Creator: Halling, A. M.
Partner: UNT Libraries Government Documents Department

The linkage of Zlib to Teapot for auto-differentiation map extraction and nonlinear analysis

Description: The differential Lie algebraic numerical library, Zlib has been linked to Teapot, the accelerator simulator code. This makes possible the use of the operational correction features of Teapot to produce a corrected lattice, and then choose either map or thin element-by-element tracking for tracking studies. Thin-element tracking is more accurate but slower than map tracking; therefore, the option of choosing one or the other is very desirable.
Date: May 1, 1993
Creator: Sun, N.; Yan, Y. T.; Pilat, F. & Bourianoff, G.
Partner: UNT Libraries Government Documents Department

Summary of dipole field angle measurements on 50mm-aperture SSC Collider Dipole Magnet Protoypes

Description: At several stages in the production of the SSC collider dipole magnets and their final installation the magnetic field angle needs to be known. A simple device using a permanent magnet which aligns itself with the magnetic field had been developed at FNAL to survey the direction of the magnetic dipole field with respect to the vertical (as determined by gravity) along the magnet axis. The determination of the dipole field angle was part of the field quality characterization of a series of thirteen full-length 50mm-aperture SSC Collider Dipole Magnet Prototypes which were built for R&D purposes at FNAL. Measurements with the first developed FAP system were performed on a regular basis through several stages of the magnet production process with the intention of fabrication quality control. Part of these included measurements performed before and after cryogenic testing: these data are summarized here. The performance of a second system with an improved probe and data acquisition system was tested on part of the DCA series as well. This paper includes a presentation of time stability, noise and angular resolution data of this second probe. Another alternative instrument to determine the dipole field angle is the ``mole`` rotating coil system developed at BNL used mainly to measure the multipole components of the magnetic field. In the case of magnet DCA320, a comparison is made between the field angle as determined by the mole and those determined by both of the FAPS.
Date: May 1, 1993
Creator: Marks, J.; DiMarco, J.; Kuzminski, J.; Ogitsu, T.; Zheng, H.; Bleadon, M. et al.
Partner: UNT Libraries Government Documents Department

Test of Fermilab built, post-ASST, 50-mm-aperture, full length SSC dipole magnets

Description: During 1992 at Fermilab, a series of nine 50-mm-aperture, 15-m-long, SSC superconducting dipole magnets, designed jointly by Fermilab, Brookhaven National Laboratory, and the SSC Laboratory, have been built and successfully cold tested. Seven of these dipole magnets, designate for the Accelerator System String Test (ASST) carried out at SSCL in Dallas, were assembled Fermilab by General Dynamics personnel, and have achieved the nominal operating current level without significant training. In addition, a series of four R&D magnets (DCA320 323) we manufactured at Fermilab to test an alternative insulation schemes. In this paper we present th quench performance of these four R&D magnets, which were cold tested at the Fermilab Magnet Test Facility at nominal temperatures of 4.35 K, 3.85 K, and 3.50 K. An extended characterization test was performed on one of these magnets (DCA322). During this test the magnet was successfully cooled down to superfluid He temperature (1.8 K) and reached a field B {ge} 9.5 T.
Date: May 1, 1993
Creator: Kuzminski, J.; Akhmetov, A. & Bossert, R.
Partner: UNT Libraries Government Documents Department

Study of stability of beam in the Fermilab main injector

Description: The Fermilab Main Injector is a new 150 GeV proton synchrotron, designed to replace the Main Ring and improve the high energy physics potential of Fermilab. The status of the Fermilab accelerator complex upgrade will be discussed. Study of the stability of the beam in the Main injector will be discussed. Detuning and corrector scheme to improve the dynamic aperture of the Main Injector will be presented. Tune modulation caused by octupolar detuning will be discussed.
Date: April 1, 1993
Creator: Mishra, C. S. & Harfoush, F.
Partner: UNT Libraries Government Documents Department

Design for low beam loss in accelerators for intense neutron source applications

Description: Control of beam loss in intense ion linacs involves keeping beam spill below parts in 10{sup {minus}5}--10{sup {minus}8}/m by preventing total beam size from extending to the limiting apertures. Starting from good rms design practices, new analysis of the machine architecture is described in terms of the effects of the machine tune with space-charge, free-energy constraint, and halo-producing mechanisms. It is shown that halos are produced by the time- (or position-) varying nature of common linac aspects (such as misalignment, mismatching, acceleration, and construction techniques) through collective core/single-particle interaction dynamics plus resonances.
Date: June 1, 1993
Creator: Jameson, R. A.
Partner: UNT Libraries Government Documents Department

Coupling impedance of vacuum pumping holes for the APS storage ring

Description: The coupling impedance of a single slot in a thick wall beam pipe was measured. The slot dimension is small compared to the wavelength of interest. The measurements were done by the wire method with the synthetic pulse technique. Gating technique was also applied to obtain the reflection response for a structure that does not have appropriate calibration standards. The measured results are in good agreement with calculated impedance using analytical formulae given by other authors.
Date: July 1, 1993
Creator: Zhou, J.; Song, J. J. & Kustom, R. L.
Partner: UNT Libraries Government Documents Department

Large aperture quadrupoles for RHIC interaction regions

Description: The ultimate luminosity performance of the Relativistic Heavy Ion Collider (RHIC) depends on the field quality in the large aperture (130 mm) superconducting quadrupoles in the interaction regions. In this paper we discuss the design features that are incorporated to obtain a good field quality. Coil midplane gap and pole shims may be adjusted to remove certain field harmonics due to systematic errors in construction. Iron tuning shims will be inserted at eight strategic locations in the assembled magnets to correct the measured values of harmonics in each magnet. The performance of two prototype magnets and upgrades under consideration will be discussed.
Date: September 1, 1993
Creator: Gupta, R.; Anerella, M. & Ganetis, G.
Partner: UNT Libraries Government Documents Department

Quench propagation study for the BNL-built, full-length, 50mm aperture SSC model dipoles

Description: As part of the program to build and test SSC 50mm aperture prototype dipole magnets, a series of seven full-length dipoles were built and tested at BNL. Important part of the testing program was the study of quench propagation velocity and hot spot temperature over a range of experimental conditions in order to characterize the safety of the conductor during quenches experienced under different circumstances. Such studies are important tools in design, implementation, and verification of quench protection strategies in superconducting accelerator magnets. This investigation was facilitated by artificially inducing quenches under controlled experimental conditions with spot heaters placed at carefully chosen locations on the magnet coils. Such studies were done as part of the 15m-long magnet test program and were performed on five of the magnets in the series. All were equipped with spot heaters on an inner coil, and two of these also had spot heaters on an outer coil. Therefore, in addition to the studies in the inner coils, it was also possible to study quench propagation in the outer coils, where slower quench velocities and higher conductor temperatures are expected, in comparison to that in the inner coils. In spontaneous quenches, where there may be no voltage taps, it is not possible to measure the conductor hot spot temperature. It is straightforward to measure the number of MIITs generated, since only the magnet current and voltage need be measured. The concept of MIITs then becomes a valuable diagnostic tool which can characterize the temperature behavior of a conductor during quench and can be used to determine limits for safe operation of the coil. With spot heaters placed at known locations and closely bracketed by voltage taps, hot spot temperature can be measured. Research such as is described in this paper is therefore important in order to ...
Date: September 1, 1993
Creator: Muratore, J.; Anerella, M. & Cottingham, G.
Partner: UNT Libraries Government Documents Department